10.3.1 tar

Because tar is used so much, and for quite a bit in addition to backups, it is being described here. For more details, see the tar manual page; instructions for viewing manual pages can be found in section 5.1 on page 121.

tar is an archiver. This means that tar can take many files and combine them all into one large file or write them out to a backup device such as a tape drive. Once you have this one large file, you will often want to compress it; the -z option is great for this. Hence, tar offers a great way to distribute programs and data on the Internet, and you’ll find that it is used extensively for this purpose.

Here’s a sample tar command line:

tar -zcvf myfiles.tar.gz /usr/local/bin

Let’s take a look at how this command can be broken down:

tar

Name of the command.

-

Tells tar that options will follow.

z

Tells tar to use gzip compression automatically; if you use this, it’s good to add a .gz extension as well.

c

Tells tar to create a new archive.

v

This says to be verbose; that is, it tells tar to let you know what it’s doing while it creates the archive.

f

This indicates that the next thing on the command line is the name of the file to be created or the device to be used. If I used /dev/st0 here, for instance, it would write the backup to the tape drive.

myfiles.tar.gz

This is the name of the file to be created.

/usr/local/bin

This is the name of the file or directory to store in the archive. It’s also possible to specify several items here.

You may often find tar.gz files (or simply tgz files) on the Internet. You can unpack these with a command like:

tar -zxvf filename.tar.gz